FIG. 20 illustrates one example of a conventional engine as disposed in a vehicle. In this engine 202, a cylinder head 206 is disposed on a cylinder block 204. A head cover 208 is positioned on the cylinder head 206. A lower case 212 is positioned below the cylinder block 204 and cooperates therewith for rotatably supporting a crankshaft 210 which extends lengthwise of the engine along its rotational axis A. An oil pan 214 is provided below the lower case 212. A baffle plate 216 is located in the oil pan 214. A crank chamber 218 is defined between the cylinder block 204 and the lower case 212.
One end of a connecting rod 220 of the engine 202 is connected to an eccentric crank of the crankshaft 210, and the other end thereof is linked to a piston 222 which is reciprocally supported in a cylinder 224. A plurality of crank-connecting rod-piston-cylinder arrangements are disposed in sidewardly spaced relation along the length of the engine in a conventional manner.
As illustrated in FIGS. 21 and 22, the cylinder block 204 is provided with: sleevelike cylinder-retaining sections 226 for press-fitting the cylinders 224 therein; block-side journal sections or walls 228 located below the cylinder-retaining sections 226 for rotatably supporting the crankshaft 210; and block-side skirt sections or walls 230 connected to the block-side journal sections 228. The skirt section 230 has a lower case-mating part 232 provided at a lower end thereof which defines a lower case-mating surface 234. Reference numeral 236 denotes a block-side blow-by gas passage.
A valve-driving mechanism 240 (FIG. 20) in the cylinder head 206 is disposed in a valve drive chamber 238. In addition, the cylinder head 206 has a head-side blow-by gas passage 242 provided therein for communicating the block-side blow-by gas passage 236 and the valve drive chamber 238 with one another. A breather chamber 244 is provided in the head cover 208 which communicates with the head-side blow-by gas passage 242. The breather chamber 244 communicates with one of an intake system or, e.g, a throttle body 246.
Referring now to FIGS. 23-27, the lower case 212 is provided with: case-side journal sections or walls 248 for rotatably supporting the crankshaft 210 in conjunction with the block-side journal sections 228; and case-side skirt sections 252 connected to the case-side journal sections 248 by means of ribs 250. The case-side skirt section 252 has a block-mating part 254 provided on the top thereof which defines thereon a top block-mating surface 256. In addition, the case-side skirt section 252 has an oil pan-mating section 258 provided on the bottom thereof which defines thereon an oil pan-mating surface 260. Reference numeral 262 denotes a case-side blow-by gas passage; 264 a case-side oil drop passage; 266 an oil pump; and 268 an oil strainer.
Turning now to FIGS. 28 and 29, the oil pan 214 is illustrated and includes a bottom portion 270 and a peripheral wall or skirt portion 272. The peripheral wall portion 272 has a lower case-mating flange 274 provided on the top thereof which defines a lower case-mating surface 276. The baffle plate 216 is provided in the oil pan 214 supported on the peripheral wall portion 272, and is offset downwardly from the lower case-mating surface 276 toward the bottom portion 270. The baffle plate 216 has a strainer-adapted hole 278 formed therethrough for inserting the oil strainer 268 therethrough.
As illustrated in FIG. 20, in the engine 202, the crank chamber 218 is oriented in a plane perpendicular to the crankshaft axis is formed into a substantially trapezoidal shape by means of the block-side skirt sections 230 and the case-side skirt sections 252, both of which skirt sections are substantially planar-shaped. The crankshaft 210 and the lower ends of the connecting rods 220 are rotated in the crank chamber 218.
Examples of such a crank chamber structure are disclosed in published Japanese Patent Application Laid-Open No. 4-276163, Japanese Utility Model Application Laid-Open No. 2-103153, and Japanese Utility Model Application Laid-Open No. 3-122210.
According to above-mentioned Application No. 4-276163, a ladder frame structure is provided in which both ends of a plurality of shaft-supporting caps are successively arranged on side walls for supporting a crankshaft from below. The side walls mate with skirt portions of a cylinder block. The ladder frame structure is characterized by a linear-shaped connecting beam which is oriented in the axial direction of the crankshaft for connecting lower portions of the aforesaid caps together. The connecting beam consists of a single member.
According to above-mentioned Application No. 2-103153, a lower case structure is provided for covering lower portions of independent main bearing caps which cooperate with crank journals in a cylinder block. The lower case structure is characterized by a lower case which is fixed to the cylinder block by fixing bolts. The lower case includes the following: a mounting flange portion which is mountable on the cylinder block by being brought into contacting engagement with a lower edge of the cylinder block; an underside-supporting portion which is forced into impinging engagement with the underside of the main bearing cap; and a stomach portion positioned on the peripheries of rotational loci of a crank counterweight and a connecting rod. The stomach portion connects the mounting flange portion and the underside-supporting portion with one another. The stomach portion has a semi-circular shape in cross-section. Further, one of the aforesaid fixing bolts penetrates both the underside-supporting portion and the main bearing cap. The other of the fixing bolts is driven through the aforesaid mounting flange portion.
According to aforesaid Application No. 3-122210, a lower block is provided in which skirt portions and bearing cap portions are integrally combined together. The lower block is characterized by arcuate ribs which extend from the skirt portions for connecting between the bearing cap portions so as to be spaced from rotational loci of the crankshaft webs and the connecting rods. The lower block also has a return opening for return oil provided at a position of the rib where a fresh air-introducing passage for ventilating blow-by gas is absent, between the bearing cap portions around the lower run of crankshaft rotation.
Other examples of crank chamber structures are disclosed in published Japanese Patent Application Laid-Open No. 6-29537 and Japanese Utility Model Application Laid-Open No. 1-113116.
According to above-mentioned Application No. 6-29537, an engine block having cylinders arranged in a V-shaped configuration is provided with upper and lower sections of a crank case. The lower section is provided with outer case walls which are opposed and parallel to each other. In addition, both ends of semi-cylindrical-shaped inner case walls are connected to the top of the outer case walls. The inner case walls extend along outlines of the connecting rods. As a result, a crank chamber is partitioned from an oil reservoir. Further, the inner case walls are provided with a plurality of passages which communicate with the oil reservoir.
According to aforesaid Application No. 1-113116, a slanted engine is provided in which bearing caps are coupled to a cylinder block, thereby supporting a crankshaft. The engine is characterized in that a curvilinear baffle plate and the bearing caps are integrally formed together between bearing portions of the bearing caps. The baffle plate is separated from an oil surface along rotational loci of the connecting rod and the crank weight. In addition, an oil return hole opens at an upper portion of the baffle plate. Further, a blow-by gas passage is punched at the upper portion of the baffle plate. The passage is positioned toward the oil pan rather than the baffle plate.
Attention is now directed to a construction of the crank chamber 218 of the engine 202 and, as illustrated in FIGS. 23-27, the lower case 212 has large openings 280 positioned between the opposed case-side skirt sections 252. The openings 280 are in communication with the oil pan 216. In addition, the oil pan-mating surfaces 260 are provided at the bottom of the skirt sections 252.
FIG. 30 illustrates another construction of the crank chamber 218, in which the cylinder block 204 is provided with block-side skirt sections 230 which have a substantially semi-cylindrical shape. The skirt sections 230 are directed in the axial direction of the crankshaft 210, and the lower case 212 is provided with case-side skirt sections 252 which have a substantially semi-cylindrical shape. The case-side skirt sections 252 mate with the block-side skirt sections 230, thereby forming a generally cylindrical-shaped crank chamber 218.
However, a problem with the lower case 212 illustrated in FIGS. 23-27 is that the openings 280 are so wide that the oil pan-mating surfaces 260 are enlarged. As a result, the cylinder block rib and the lower case 212 are reduced in rigidity and strength, although serving as a case which surrounds the crankshaft 210 and the connecting rods 220. This causes an inconvenience in that such reduced rigidity and strength is a source of vibratory noise which occurs when the engine is run.
A further problem with the planar-shaped skirt sections 230, 252 shown in FIGS. 21-27 as well as the cylindrical-shaped skirt sections 230, 252 shown in FIG. 30 is that a surface area of the case enclosing the crankshaft 210 and the connecting rods 220 is increased. This causes further inconveniences in that such an increased surface area involves increases in weight and cost, and further, since the planar shape is responsible for reduced rigidity and strength, such an increased surface area is the cause of vibratory noise when the engine 202 is run.
Further, since the planar-shaped skirt sections 230 and 252 illustrated in FIGS. 21-27 form the crank chamber 218 which opens downwardly in a substantially trapezoidal shape, such configuration is liable to disturb rotational wind produced from the crankshaft 210 and the connecting rods 220, both of which are rotated in the crank chamber 218. In addition, the cubic volume of gases in the crank chamber 218 increases. Thus, when the crankshaft 210 and the connecting rods 220 are rotated, the gases are thereby stirred up, which results in air resistance. Therefore, output loss from the engine 202 increases.
Since the crank chamber 218 opens downwardly in a substantially trapezoidal shape, a spray of oil splashed in the crank chamber 218 by respective rotations of the crankshaft 210 and connecting rods 220 is blown into the oil pan 214 through the openings 280 at high speeds. Then, another problem lies in that such oil is caused to impinge on the peripheral wall portion 270 or the baffle plate 216, thereby producing aeration. This brings about yet another inconvenience in that the amount of aeration in the oil, which oil is drawn from the oil strainer 268 and is thereafter conveyed to each section of the engine 202 by means of the oil pump 266, increases, thereby reducing the lubricating performance of the engine 202.
In the crank chamber 218, the spray of oil turns to oil mist. The oil mist is moved into the breather chamber 244 in the head cover 208 after flowing through the case-side blow-by gas passage 262, the block-side blow-by gas passage 236, and the head-side blow-by gas passage 242 in this order. In this case, as illustrated in FIG. 20, if the crank chamber 218 opens downwardly in a substantially trapezoidal shape, and further if a passage inlet 282 of the case-side blow-by gas passage 262 is positioned close to the oil pan 214, then an increased quantity of the oil mist is moved into the breather chamber 244. Then, still another inconvenience is that the breather chamber 244 must be made larger in cubic capacity, thereby increasing the height, weight, and cost of the engine 202.
Turning now to a construction of the crank chamber 218 illustrated in FIG. 30, the lower case 212 has wide openings 280 provided between the case-side skirt sections 252, which openings 280 communicate with an oil pan (not shown). Similarly to the above, this construction also causes inconveniences in that the reduced rigidity and strength as earlier mentioned contribute to vibratory noise when the engine 202 is run. Further, such splashed oil as previously described reduces the lubricating performance of the engine 202, with consequential increases in the height, weight, and cost of the engine 202.
As illustrated in FIGS. 23-27, the case-side journal sections 248 in the lower case 212 are connected at both ends thereof to the respective case-side skirt sections 252 by means of a pair of ribs 250. The journal section 248 is thereby integrally combined at both ends thereof with the block-mating sections 254 and the oil pan-mating sections 258. The former mating section 254 is positioned on the top of the skirt section 252, while the latter mating section 258 is located on the bottom of the skirt section 252. As a result, the case-side journal section 248 is supported at both ends thereof on the skirt sections 252, the block-mating sections 254, and the oil pan-mating sections 258, which sections 252, 254, and 258 are remote from the axis of the crankshaft 210. As a result, support in the axial direction of the crankshaft 210 is insufficient when the engine 202 is run. This causes an inconvenience in that the journal section 248 is deformed in the axial direction of the crankshaft 210, resulting in vibratory noise.
As illustrated in FIGS. 23-27, the lower case 212 is provided with the planar-shaped case-side skirt portions 252 which extend from the block-mating sections 254 to the oil pan-mating sections 258. The lower case 212 also has the wide openings 280 positioned between the skirt sections 252, which openings 280 communicate with the oil pan 214. Referring now to the lower case 212 as shown in FIG. 30, planar-shaped case-side outer skirt sections 284 are positioned in outward directions of the semi-cylindrical case-side skirt sections 252. The outer skirt sections 284 extend from the block-mating sections 254 to the oil pan-mating sections 258. In addition, the wide openings 280, which communicate with the oil pan 214, are provided between the case-side skirt sections 252.
In the lower case 212, the planar skirt section 252 extending between the mating sections 254 and 258 is thereby formed into a longitudinal face. Such longitudinal face is reduced in rigidity in a direction in which the longitudinal face is bent. Consequently, the skirt section 252 experiences greater deformations due to vibration incurred with operation of the engine 202. This causes inconveniences in that such vibrations are conducted to the oil pan 214, resulting in noise emission, or resulting in breakage of the baffle plate 216, depending upon the shape of the baffle plate 216.
In the lower case 212 shown in FIG. 30, the semi-cylindrical case-side skirt sections 252 and the planar case-side outer skirt sections 284 are connected together at the block-mating sections 254. As a result, two wall portions are formed adjacent to the block-mating sections 254. This creates a problem in that such wall portions are useless sections. Further, in the lower case 212 illustrated in FIG. 30, the skirt section 252 has an oil drop hole 286 provided therethrough. This causes an inconvenience in that the skirt section is reduced in rigidity, thereby emitting the vibratory noise.
As shown in FIG. 23, the lower case 212 has case-side mounting boss portions 290 arranged on the block-mating sections 254 for sealing block-adapted outer seal surfaces 288 of the block-mating surfaces 256. However, the seal surfaces 288 are provided so as to deviate from the axis which extends between the centers of the boss portions 290. In addition, the boss portions 290 are provided at respective positions spaced apart from the ribs 250. The ribs 250 support the journal sections 248 on the case-side skirt sections 252, the block-mating sections 254, and the oil pan-mating sections 258. As a result, an inconvenience arises in that the lower case-mating surfaces 234 of the cylinder block 204 and the block-mating surfaces 256 of the lower case 212 cannot be fitted together with sufficient surface pressure, resulting in a reduction in sealing performance, because the block-adapted outer seal surfaces 288 are displaced from the axis extending between the centers of the boss portions 290. A further inconvenience is that, when the engine 202 is run, then the mounting boss portions 290 permit transmission of vibration caused by the crankshaft 210 directly to the oil pan-mating sections 258 and the case-side skirt sections 252 from the case-side journal sections 248, resulting in the vibratory noise, because the boss portions 290 are not directly connected to the above-described ribs 250, but instead are spaced apart therefrom.
As shown in FIG. 25, in the lower case 212, a passage inlet 282 of the case-side blow-by gas passage 262 and a passage outlet 292 of the case-side oil drop passage 264 are positioned adjacent to the journal section 248, and are further oriented in a direction toward the oil pan 214 beneath the passages 282 and 292. As a result, oil falling from the oil drop passage 264 drops directly into the oil pan 214, and then collides therewith. Then, one problem is that oil mist and aeration are liable to occur. Further, blow-by gas containing a large amount of the oil mist near the crankshaft 210 is drawn from the inlet 282 of the oil drop passage 264, and then the oil mist is moved into the breather chamber 244 in large quantities. For this reason, the breather chamber 244 must be made larger in cubic volume. This causes an inconvenience due to an increase in the height, weight, and cost of the engine 202. Another inconvenience lies in that oil containing the aeration is drawn from the oil strainer 268, and then the aeration in the oil fed to each section of the engine 202 by means of the oil pump 266 increases in quantity, thereby reducing the lubricating performance of the engine 202.
Referring to FIG. 26, the lower case 212 has a strainer-mounting boss portion 294 positioned on the oil pan-mating surface 260. As illustrated in FIG. 27, the oil strainer 268 is directly mounted on the boss portion 294. In addition, a bracket-mounting boss portion 296 is provided on the oil pan-mating surface 260, and the oil strainer 268 is indirectly mounted on the bracket-mounting boss portion 296 through a strainer-adapted bracket 298. As a result, the oil strainer 268 experiences a large amount of deformation from the case-side journal section 248 because the oil strainer 268 is mounted on the journal section 248 which is subject to deformation due to vibration from the crankshaft 210 when the engine 202 is run. For this reason, the strength of the oil strainer 268 and the strainer-adapted bracket 298 must be increased, which causes another inconvenience of increased weight and cost.
As illustrated in FIGS. 28 and 29, the oil pan 214 has the baffle plate 216 mounted on the peripheral wall portion 272. The baffle plate 216 is positioned toward the bottom 270 rather than the lower case-mating surface 276. In addition, a strainer-adapted hole 278 opens through the baffle plate 216, through which the oil strainer 268 is inserted. As a result, there is an inconvenience in that the oil pan 214 requires a working process including mounting the baffle plate 216 on the oil pan 214, with a concomitant rise in cost of the oil pan 214. Further, since the strainer-adapted hole 278 which receives the oil strainer 278 is included on the baffle plate 216, then the oil dropping from the aforesaid hole 278 produces aeration near a strainer suction opening 300. This causes a further inconvenience in that the quantity of aeration in the oil increases, thereby reducing the lubricating performance of the engine 202.
Moreover, since the baffle plate 216 is mounted on the peripheral wall portion 272 so as to entirely cover the bottom 270 of the oil pan 214, this causes an inconvenience due to the increased dimension, weight, and cost of the baffle plate 216, and another inconvenience as a source of noise emission. Further, since the baffle plate 216 is mounted on the peripheral wall portion 272 at a position toward the bottom 270 rather than the lower case-mating surface 276, and is further spaced apart from the revolving crankshaft 210 and the connecting rods, then rotational wind from the crankshaft 210 and the connecting rods 220, both of which are rotated in the crank chamber 218, is subject to disturbance. In addition, gases in the crank chamber 218 are increased in cubic volume. Then, when the crankshaft 210 and the connecting rods 220 are rotated, the gases are thereby stirred up, which results in air resistance. This creates another inconvenience of increased output loss from the engine 202.